Floating heatsink for removable components

ABSTRACT

A floating heatsink is disclosed for components mounted within an electromagnetic enclosure. The floating heatsink includes an aperture within the enclosure wall against which a floating heatsink is disposed on the interior of the enclosure. The floating heatsink is dimensioned to overlap the enclosure around the aperture. A resilient bias member is disposed along the overlap between the floating heatsink and the enclosure. The resilient bias member acts as an electromagnetic gasket while urging the floating heatsink against the component. In certain embodiments the component is replaceable via a second aperture in the enclosure. The floating heatsink is particularly useful for overcoming the need for thermal compounds of heatsinks using the enclosure known in the art.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/945,075, filed on Sep. 20, 2004, and owned in commonherewith.

FIELD OF THE INVENTION

The present invention relates to a floating heatsink for removablecomponents and is particularly concerned with heatsinks for componentsrequiring removal for servicing or replacement.

BACKGROUND OF THE INVENTION

Heat dissipation is a by-product of most modern electronic equipment,and when heat dissipation from a component or assembly is sufficientlylarge, heatsinks are used to keep the component or assembly at asufficiently low temperature.

An additional requirement of high-speed electronics is the containmentand/or shielding of electromagnetic radiation developed by the circuitryduring operation. Such electromagnetic radiation can disturb thefunctioning of other nearby electronic equipment, and vice versa. Inorder to contain electromagnetic radiation, it is known in the art toprovide enclosures which either block or greatly attenuate emissionsfrom a circuit in operation.

Under some circumstances, the electromagnetic containment enclosure canserve as a heatsink for components mounted within the enclosure.Typically, components are mounted within a circuit board within theenclosure, and means, such as a compliant thermal compound, are used tobridge gaps between a component and the enclosure wall that is to beused as a heatsink.

This approach does not provide for ready heatsinking of removablecomponents, as there is no simple method for ensuring adequatereplacement of the thermal compound when a component is replaced.

In view of the foregoing, it would be desirable to provide a techniquefor allowing removal of components from an electromagnetic enclosurewhich overcomes the above-described inadequacies and shortcomings, byproviding a mechanism which does not require a compliant thermalcompound replacement but does provide heatsinking of the removablecomponent and integrity of the electromagnetic enclosure.

SUMMARY OF THE INVENTION

According to an aspect of the present invention there is provided anapparatus for removing heat from a component to be mounted within anenclosure, where the enclosure has a first aperture adjacent to thecomponent when the component is in an operating position. The apparatushas a floating heatsink disposed interior to the enclosure adjacent tothe first aperture, and the floating heatsink is dimensioned to overlapthe enclosure around the periphery of the first aperture. There is alsoa resilient bias member disposed between at least a portion of anoverlap between the floating heatsink and the enclosure, wherein theresilient bias member acts as an electromagnetic gasket between thefloating heatsink and the enclosure and whereby the resilient biasmember urges the floating heatsink against the component in theoperating position.

In one aspect, the present invention provides a controllable thermalcontact to a removable component while maintaining electromagneticshielding integrity of the enclosure.

In one embodiment, the resilient bias member may be a formed metallicstrip. The formed metallic strip may have a plurality of fingers, andthe formed metallic strip may have a plurality of formed ridges. Inanother embodiment, the resilient bias member may be formed from anelastomeric compound having electrically conductive media dispersedtherethrough.

Further, in some embodiments there may be provided a second resilientbias element to augment the bias provided by the resilient bias member.The use of a second resilient bias element provides an additional degreeof control of the urging of the floating heatsink against the component.

In accordance with another aspect of the present invention there isprovided a method for removing heat from a component to be mountedwithin an enclosure. The enclosure has a first aperture adjacent to thecomponent when the component is in an operating position and the methodcomprises the steps of disposing interior to the enclosure a floatingheatsink adjacent to the first aperture. The floating heatsink isdimensioned to overlap the enclosure around the periphery of the firstaperture. The method further comprises the step of disposing a resilientbias member between an overlap between the floating heatsink and theenclosure, wherein the resilient bias member acts as an electromagneticgasket between the floating heatsink and the enclosure. Further, by theaction of the resilient biasing member, the floating heatsink is urgedagainst the component, when the component is in the operating position.

The present invention will now be described in more detail withreference to exemplary embodiments thereof as shown in the appendeddrawings. It should be recognized that the diagrams are not intended toconvey any indication of scale. While the present invention is describedbelow including preferred embodiments, it should be understood that thepresent invention is not limited thereto. Those of ordinary skill in theart having access to the teachings herein will recognize additionalimplementations, modifications, and embodiments which are within thescope of the present invention as disclosed and claimed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further understood from the following detaileddescription of embodiments of the invention and accompanying drawings inwhich:

FIG. 1 is a perspective view of a component and heatsink assemblyaccording to the prior art.

FIG. 2 is a perspective view from the bottom of a fixed portion of aheatsink assembly according to an embodiment of the invention.

FIG. 3A is a perspective view from the top of a movable portion of aheatsink assembly according to an embodiment of the invention.

FIG. 3B is a perspective view from the top of a movable portion of aheatsink assembly according to another embodiment of the invention.

FIG. 4 is a exploded perspective view from the top of a heatsinkassembly according to an embodiment of the invention.

FIG. 5 is a perspective view from the top of a heatsink assembly andremovable component according to an embodiment of the invention.

FIG. 6 is a cross-sectional view of the heatsink assembly of FIG. 5taken along section line 2 of FIG. S.

DETAILED DESCRIPTION

Certain terminology may be employed in the description to follow forconvenience rather than for any limiting purpose. For example, the terms“top”, “bottom”, “forward”, “rearward”, “right”, “left”, “rightmost”,“leftmost”, “upper”, and “lower” designate directions in the drawings towhich reference is made. Terminology of similar import other than thewords specifically mentioned above is likewise to be considered as beingused for purposes of convenience rather than in any limiting sense. Inthe description and figures to follow, corresponding characters are usedto designate corresponding elements throughout the several views, withequivalent elements being referenced with prime or sequentialalphanumeric designations where appropriate to assist understanding.

Modern electronic circuit assemblies are progressively moving towardsdenser and denser concentrations of heat generating components withingiven package sizes. Increased density brings a need for enhanced meansto remove heat, and as well, means to contain electromagnetic radiationgenerated by the circuitry during its operation. One approach known inthe art is to completely enclose the electronic circuit board andattendant circuitry with a thermally conductive and electromagneticradiation containing enclosure. A common term for such an enclosurewhich conforms relatively closely to the dimensions of a circuit card isthat of a “clamshell”. The clamshell enclosure has additional advantagesin assisting in preventing penetration of exterior interferingradiation, such as that from adjacent circuit assemblies, frominterfering with circuitry within the enclosure.

A relative disadvantage of a clamshell enclosure is the difficulty inreplacing components. Within telecommunications systems, there areelectronic assemblies with subassemblies which may have an operationallife significantly less than the life of the remainder of the assembly.One example is the laser transceivers used in modern optical networkingequipment. With a clamshell enclosure which contains multiple such lasertransceiver assemblies, the failure of one assembly would require theremoval of the entire clamshell if the failed assembly were to bereplaced. Clearly, it would be desirable to have a clamshell enclosurewhich would admit removable subassemblies. However, in the case of lasertransceiver assemblies, for example, there is a strong need foreffective heatsinking of the transceiver assembly. In an assembly withpermanently mounted transceivers, it is common in the art to use thewall of the clamshell enclosure as a heatsink, and appropriate means forsecuring the transceiver in good thermal contact with the wall are used.

In the case of removable assemblies, it is necessary to be able toremove the subassembly, yet when the subassembly is mounted inoperational position, to also ensure adequate thermal contact.

Referring to FIG. 1A there may be seen an exploded view of a circuitboard 180 having mounted thereon a frame 182, a heatsink 184, and a clipassembly 186. The frame 182 serves as a mounting enclosure for aremovable component or assembly, while heatsink 184 is mechanicallyattached to frame 182 via clip assembly 186. Not shown is a connectormounted on circuit board 180, to which the removable component connectsupon insertion into frame 182. Referring to FIG. 1B, there may seen aperspective view of the heatsink 184, secured to frame 182 with clip186, while removable component 110 is shown prior to mounting withinframe 182. In FIG. 1C, removable component 110 is shown mounted withinframe 182. In the mounted position, heatsink 184, in mechanical contactwith removable component 110, acts to reduce thermal resistance fromremovable component 110 to the ambient environment, thereby dissipatingheat generated within removable component 110. The resulting reductionin temperature rises within removable component 110 act to keeptemperatures within operational limits and enhance long term reliabilityof removable component 110, as is well known in the art.

One possible problem with the approach diagrammed in FIG. 1 is thesliding friction occurring between heatsink 184 and the removablecomponent 110. Close mechanical contact between removable component 110and heatsink 184 is necessary for good thermal flow, howevermanufacturing tolerances work against achieving the necessary fit.Intermediate resilient thermally conductive materials may be used tomediate the gap resulting from manufacturing tolerances, however thehigh coefficient of friction that results from use of such materialsresults in unacceptably high forces being generated upon insertion andremoval of removable component 110.

Referring to FIG. 2, there may be seen a perspective view from thebottom, of one side 200 of a clamshell enclosure. On the enclosure side200 may be seen mounting holes 202, for securing the enclosure side 200to the circuit board and opposite side of the enclosure. Also visible isaperture 204, an opening in enclosure side 200, for the receiving of afloating heatsink which will be described below. Mounting tabs 206, atthe front of enclosure side 200, are for the installation of cardejectors (not shown), mechanical latches which assist in insertion andremoval of the clamshell assembly upon installation. The clamshellenclosure is conveniently made from a castable, extruded or machinedaluminum alloy, providing both thermal conductivity and electromagneticinterference shielding.

Reference is now made to FIG. 3A, which shows a floating heatsink 330having a resilient bias member 332 disposed on the top surface offloating heatsink 330 around its periphery. In this embodiment, theresilient bias member 332 is an electromagnetic gasket formed from anelastomeric compound having electrically conductive media disbursedtherethrough. The electromagnetic gasket acts so as to containelectromagnetic energy within the clamshell enclosure. Resilient biasmember 332 also operates to urge floating heatsink 330 downwards againsta removable component. In particular, the floating heatsink 330 isdimensioned larger than the aperture 204 (FIG. 2) within the clamshellenclosure. Accordingly, the floating heatsink 330 is dimensioned suchthat its periphery overlaps with the enclosure side 200 (FIG. 2) of theclamshell enclosure surrounding the aperture 204. Thus, the resilientbias member 332 is disposed between the enclosure side 200 of theclamshell enclosure and the peripheral overlap portion of the floatingheatsink 330. Resilient bias member 332 acts against the underside ofthe clamshell enclosure so as to urge the floating heatsink 330downwards against a removable component. Although in this embodiment,resilient bias member 332 is formed of an elastomeric compound, ingeneral any resilient gasketing material known to those skilled in theart having a compression-set over its operating life sufficient toprovide an appropriate biasing force to provide good thermal contactagainst a removable component while providing adequate electromagneticinterference gasketing could be employed.

Under certain applications, the amount of bias provided by the resilientgasketing material may be insufficient to provide the amount of biasdesired. In these circumstances an additional bias element 340, forexample a separate spring element, may be used to augment the biasprovided by the resilient gasketing material that makes up the resilientbias member 332. Such an additional bias element 340 may comprise aspring element running parallel to the resilient gasketing material, ora plurality of spaced smaller springs, for example. The additional biaselement 340 may be disposed in a channel 334 formed between theresilient bias member 332 and an upper portion of the floating heatsink330.

It is also clear that certain applications, for example circuitry havinglow frequency signals, may not require a continuous gasket around theperiphery of the overlap. In this case, the resilient gasketing materialmay be disposed only over a portion of the overlap, or at a plurality ofdiscontinuous portions, insofar as the emissions or susceptibilityrequirements regarding electromagnetic leakage through any gaps meet therequirements of the particular apparatus.

Reference is now made to FIG. 3B, which shows another embodiment of afloating heatsink 330 with resilient bias member 332. In thisembodiment, resilient bias member 332 includes a multi-fingered metallicgasketing strip surrounding the periphery of floating heatsink 330. Themetallic gasketing strip is formed from a plurality of fingers or ridges338 (individually indicated as 338 a, 338 b, . . . , 338 n). Thesuccession of fingers or ridges 338 within the ridged metallic gasketingstrip provides resilience as well as effective electromagneticshielding. The fingers or ridges 338 bias the floating heatsink 330 in adownward direction relative to the surrounding clamshell enclosure bybearing against the enclosure side 200 surrounding the aperture 204within the clamshell enclosure.

Referring to FIG. 4, there may be seen an exploded perspective view of aclamshell enclosure using a floating heatsink according to an embodimentof the invention. A top side clamshell enclosure portion 420 issecurable to a bottom side clamshell enclosure portion 421. Circuitboard 400, located within the clamshell enclosure when top side 420 issecured to bottom side 421, has component frame 402 mounted thereon.Component frame 402, for receiving a removable component, is mountedadjacent aperture 423 which is located on a front face of bottom sideenclosure portion 421. Upon assembly of the clamshell enclosure,floating heatsink 430 mounts within aperture 424 in top side clamshellenclosure portion 420, immediately adjacent component frame 402. Inoperation, resilient bias member 432 urges floating heatsink 430 againsta component housed within frame 402. Resilient bias member 432 alsoprovides an electromagnetic interference gasket function within the gapbetween floating heatsink 430 and top side clamshell enclosure portion420.

Referring to FIG. 5, there may be seen an assembled clamshell enclosure525, having a removable component 510 in position for insertion intoaperture 523. Upon insertion into aperture 523, removable component 510passes into the component frame (not seen in this diagram) and bearsagainst floating heatsink 532. The resilient bias member mounted betweenthe top surface 520 and floating heatsink 532 urges heatsink 532 againstremovable component 510, providing good thermal contact. Also, asdescribed previously, the resilient bias member also serves as a gasket,blocking or attenuating electromagnetic radiation that might enter orexit the clamshell enclosure around the periphery of floating heatsink532.

Referring to FIG. 6A, there may be seen a cross-sectional view of FIG. 5taken at section 2 and a corresponding cross-sectional view with theremovable component 610 inserted at FIG. 6B. More specifically,clamshell enclosure 625 has top side enclosure member 620 havingaperture 624 therein. Floating heatsink 630 resides within aperture 624,having resilient bias member 632 between heatsink 630 and top sideenclosure member 620. Removable component 610, illustrated in theremoved position in FIG. 6A, upon insertion, bears against heatsink 630.In the inserted position, illustrated in FIG. 6B, resilient bias member632 urges the heatsink 630 against removable component 610, providinggood thermal contact.

As may be seen, the assemblies described above provide one skilled inthe art a method and apparatus for providing thermal contact forremovable components and maintenance of the integrity of anelectromagnetic screening enclosure so as to prevent either emissions oradmission of electromagnetic radiation. As well, the aforedescribedassemblies provide allowance for mechanical tolerances incurred inmanufacturing and over the operational life of the assembly, as well ascontrol of contact forces via the resilient bias member for properthermal and interconnection performance. Further, the described designprovides for a reduction in size over approaches which do not integratethe bias member functionality with electromagnetic gasketing. Thisreduction in size allows for greater utilization of the interior spaceof the clamshell enclosure.

While the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives,modifications, and variations will be apparent to those skilled in theart in light of the foregoing description.

For example, the floating heatsink assembly within a clamshell enclosurecould be adapted to non-removable components fixed to the circuit board,eliminating the usual need for a compliant thermal compound to fill thespace between the fixed component and the heatsink. In this type ofapplication, the elimination of the thermal compound would both simplifyinitial manufacturing processes and any subsequent repair processes.

As well, the clamshell type of enclosure exemplifies but one kind ofcontainment enclosure. It is contemplated that electronic assemblieshaving portions of the assembly enclosed, albeit not wholly as in theclamshell embodiment, could also make use of the floating heatsink forremovable components requiring heatsinking within the enclosed portion.

Therefore, what has been described are embodiments providing means formounting a removable component to a circuit pack where the circuit packis enclosed in a fixed heatsink. By utilizing a floating heatsinkmounted within an aperture of the fixed heatsink, in coordination with aresilient bias member that also acts as an electromagnetic containmentgasket, component removability is obtained while still effectingelectromagnetic shielding and thermal contact between the heatsink andcomponent.

Numerous modifications, variations and adaptations may be made to theparticular embodiments of the invention described above withoutdeparting from the scope of the invention, which is defined in theclaims. Accordingly, it is intended to embrace all such alternatives,modifications, and variations as fall within the spirit and broad scopeof the appended claims.

1. An apparatus for removing heat from a component to be mounted withinan enclosure, said enclosure having a first aperture adjacent to saidcomponent when said component is in an operating position, the apparatuscomprising: a floating heatsink disposed interior to said enclosureadjacent to said first aperture, said floating heatsink dimensioned tooverlap said enclosure around the periphery of said first aperture; anda first resilient bias member disposed between at least a portion of anoverlap between said floating heatsink and said enclosure, wherein saidfirst resilient bias member acts as an electromagnetic gasket betweensaid floating heatsink and said enclosure, whereby said first resilientbias member urges said floating heatsink against said component in theoperating position.
 2. An apparatus as claimed in claim 1, wherein saidenclosure further comprises a second aperture, and said component may beremoved from said enclosure via said second aperture.
 3. An apparatus asclaimed in claim 1, wherein said first resilient bias member comprisesan elastomeric compound having electrically conductive media dispersedtherethrough.
 4. An apparatus as claimed in claim 1, wherein said firstresilient bias member comprises a multi-fingered metallic gasketingstrip.
 5. An apparatus as claimed in claim 1, wherein said floatingheatsink includes a peripheral edge having a top surface, said topsurface facing an underside of said enclosure adjacent said aperture,and wherein said first resilient bias member is disposed atop at least aportion of said top surface.
 6. An apparatus as claimed in claim 5,wherein said first resilient bias member contacts said underside of saidenclosure and biases said floating heatsink away from said enclosure. 7.An apparatus as claimed in claim 1, further including a second resilientbias member disposed between said floating heatsink and said enclosure,said second resilient bias member bearing against said enclosure to urgesaid floating heatsink against said component in the operating position.8. An apparatus as claimed in claim 7, wherein said floating heatsinkincludes a peripheral edge having a top surface, said top surface facingan underside of said enclosure adjacent said aperture, and wherein saidfirst resilient bias member and said second resilient bias member aredisposed atop at least a portion of said top surface and bear againstsaid underside.
 9. An apparatus for removing heat from a component to bemounted within an enclosure, said enclosure having an underside surfaceand defining an aperture adjacent to said component when said componentis in an operating position, the apparatus comprising: a floatingheatsink disposed interior to said enclosure adjacent to said firstaperture, said floating heatsink being dimensioned larger than saidaperture such that a peripheral portion of said floating heatsinkoverlaps with a portion of said underside surface adjacent saidaperture; and a first resilient bias member disposed between saidperipheral portion of said floating heatsink and said portion of saidunderside surface adjacent said aperture, wherein said first resilientbias member acts as an electromagnetic gasket between said floatingheatsink and said enclosure, and wherein said first resilient biasmember bears against said underside surface to urge said floatingheatsink against said component in the operating position.
 10. Anapparatus as claimed in claim 9, wherein said enclosure furthercomprises a second aperture, and said component may be removed from saidenclosure via said second aperture.
 11. An apparatus as claimed in claim9, wherein said first resilient bias member comprises an elastomericcompound having electrically conductive media dispersed therethrough.12. An apparatus as claimed in claim 9, wherein said first resilientbias member comprises a multi-fingered metallic gasketing strip.
 13. Anapparatus as claimed in claim 9, wherein said floating heatsink includesa peripheral edge having a top surface, said top surface facing saidunderside of said enclosure adjacent said aperture, and wherein saidfirst resilient bias member is disposed atop at least a portion of saidtop surface.
 14. An apparatus as claimed in claim 9, further including asecond resilient bias member disposed between said floating heatsink andsaid enclosure, said second resilient bias member bearing against saidenclosure to urge said floating heatsink against said component in theoperating position.